A decade ago, an international effort began to understand how the Earth functioned as a system. This involved taking apart the earth's components (e.g. oceans, terrestrial ecosystems, atmosphere, hydrological systems) and studying each one separately and how they connected to, and influenced, the other parts of the earth system. This was a very successful effort that elucidated how the system worked and has permitted major advances such as improved climate prediction. Over this same ten-year period, earth system scientists began to appreciate how much human activities impact the various components of the earth system. Burning of fossil fuels result in emissions of vast amounts of carbon dioxide and other earth-warming gases that are changing the atmosphere and even the productivity of terrestrial vegetation. Fishing fleets have depleted the stock of many species, and the catches are collapsing. Irrigation and other alterations of surface and underground water are increasing the vulnerability of hydrologic systems and the people that depend on these precious water sources. Agricultural activities have resulted in massive deforestation and alteration of land cover at huge scales – with the amount of land devoted to agriculture increasing five-fold over the past three centuries. In short, human activities are so pervasive that they are capable of altering the earth system in ways that could change the viability of the very processes upon which human and non-human species depend.
As recognition began to be given to the important role of human interactions with the earth system, a vigorous set of research activities was undertaken using a combination of methods from the biophysical and the social sciences to understand these interactions. This work has been concerned with issues of tropical deforestation, with climate change and societal impacts, with the reciprocal interactions of population-environment-consumption, with large-scale monitoring of changes in vegetation and with mega-urbanization dynamics, and with historical reconstructions of human interactions at local and regional scales. This is an integrated science agenda developed in multidisciplinary fashion because of the complex nature of the problems being tackled.